Codeinone

Abstract: Opium poppy produces a diverse array of pharmaceutical alkaloids, including the narcotic analgesics morphine and codeine. The benzylisoquinoline alkaloids of opium poppy accumulate in the cytoplasm, or latex, of specialized laticifers that accompany vascular tissues throughout the plant. However, immunofluorescence labeling using affinity-purified antibodies showed that three key enzymes, (S)-N-methylcoclaurine 3'-hydroxylase (CYP80B1), berberine bridge enzyme (BBE), and codeinone reductase (COR), involved in the biosynthesis of morphine and the related antimicrobial alkaloid sanguinarine, are restricted to the parietal region of sieve elements adjacent or proximal to laticifers. The localization of laticifers was demonstrated using antibodies specific to the major latex protein (MLP), which is characteristic of the cell type. In situ hybridization showed that CYP80B1, BBE, and COR gene transcripts were found in the companion cell paired with each sieve element, whereas MLP transcripts were restricted to laticifers. The biosynthesis and accumulation of alkaloids in opium poppy involves cell types not implicated previously in plant secondary metabolism and dramatically extends the function of sieve elements beyond the transport of solutes and information macromolecules in plants.

Abstract: Summary The narcotic analgesic morphine is the major alkaloid of the opium poppy Papaver somniferum. Its biosynthetic precursor codeine is currently the most widely used and effective antitussive agent. Along the morphine biosynthetic pathway in opium poppy, codeinone reductase catalyzes the NADPH-dependent reduction of codeinone to codeine. In this study, we have isolated and characterized four cDNAs encoding codeinone reductase isoforms and have functionally expressed them in Escherichia coli. Heterologously expressed codeinone reductase-calmodulin-binding peptide fusion protein was purified from E. coli using calmodulin affinity column chromatography in a yield of 10 mg enzyme l-1. These four isoforms demonstrated very similar physical properties and substrate specificity. As least six alleles appear to be present in the poppy genome. A comparison of the translations of the nucleotide sequences indicate that the codeinone reductase isoforms are 53% identical to 6′-deoxychalcone synthase from soybean suggesting an evolutionary although not a functional link between enzymes of phenylpropanoid and alkaloid biosynthesis. By sequence comparison, both codeinone reductase and 6′-deoxy- chalcone synthase belong to the aldo/keto reductase family, a group of structurally and functionally related NADPH-dependent oxidoreductases, and thereby possibly arise from primary metabolism.

Abstract: The opium poppy, Papaver somniferum, is one of mankind's oldest medicinal plants. Opium poppy today is the commercial source of the narcotic analgesics morphine and codeine. Along with these two morphinans, opium poppy produces approximately eighty alkaloids belonging to various tetrahydrobenzylisoquinoline-derived classes. It has been known for over a century that morphinan alkaloids accumulate in the latex of opium poppy. With identification of many of the enzymes of alkaloid biosynthesis in this plant, biochemical data suggested involvement of multiple cell types in alkaloid biosynthesis in poppy. Herein the immunolocalization of five enzymes of alkaloid formation in opium poppy is reported: (R,S)-3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase central to the biosynthesis of tetrahydroisoquinoline-derived alkaloids, the berberine bridge enzyme of the sanguinarine pathway, (R,S)-reticuline 7-O-methyltransferase specific to laudanosine formation, and salutaridinol 7-O-acetyltransferase and codeinone reductase, which lead to morphine. In capsule and stem, both O-methyltransferases and the O-acetyltransferase are found predominantly in parenchyma cells within the vascular bundle, and codeinone reductase is localized to laticifers, the site of morphinan alkaloid accumulation. In developing root tip, both O-methyltransferases and the O-acetyltransferase are found in the pericycle of the stele, and the berberine bridge enzyme is localized to parenchyma cells of the root cortex. Laticifers are not found in developing root tip, and, likewise, codeinone reductase was not detected. These results provide cell-specific localization that gives a coherent picture of the spatial distribution of alkaloid biosynthesis in opium poppy.